1. Field of the Invention
This invention relates to an apparatus for processing a semiconductor wafer and more particularly to an apparatus for performing a film-forming process by means of the CVD method (the chemical vapor deposition method).
2. Description of the Related Art
Etching apparatuses and CVD apparatuses have been widely used in processes for manufacturing semiconductors. As the structure of semiconductors has recently become finer, it has become more and more important that etching accuracies and the qualities of formed films be improved, and a plurality of reactive gases have been more and more frequently used to perform required etching and form required films.
With a plasma etching apparatus, a reactive gas .is introduced into a process chamber under a reduced pressure, and semiconductor wafers are etched in a required manner by a physico-chemical reaction of the reactive gases in a plasma state. When wafers having fine processing holes are etched, it is required that the used gas after etching be removed efficiently. With the conventional etching apparatus, it is difficult to efficiently introduce an etching gas into and exhaust the same from fine processing holes.
The CVD apparatus is so constructed that a plurality of reactive gases are introduced into a process chamber under a reduced pressure and chemically react on semiconductor wafers to form predetermined thin films on them. It is known in the experimental stage that it is effective to laminate several hundred layers of extremely thin films (each about five angstroms in thickness, for example) on one after another in order to improve the film properties. With the conventional CVD apparatus, however, the process for forming such laminated films is complicated and requires a long time. It is, therefore, practically difficult to perform this process.
A so-called pulse CVD method by which two different gases are alternately supplied to the process chamber in a pulsing manner has been proposed to form reaction products of two highly reactive gasses as films on the wafers, or to form GaAs layers on the wafers by alternately laminating Ga thin films and As thin films. With this method, the thickness of the films is accurately controlled and only gas part adsorbed onto the wafer surfaces is used for film formation, resulting in the improvement of the film quality. With the conventional CVD apparatus, however, the process for supplying two gases alternately is complicated and requires a long time. Thus, it is difficult to perform the process practically with the conventional CVD apparatus.
Published Unexamined Japanese Patent Application No. 3-72077 discloses an apparatus for forming a silicon oxide film by a method similar to the pulse CVD method by using a rotary substrate holder. The apparatus as shown in FIGS. 1 and 2 of this publication has a substrate holder 2 provided in the upper portion of the inside of a vacuum chamber 1. The holder 2 carries four substrates 4 and is rotated at a high speed of about 60 rpm. The vacuum chamber 1 is divided into two compartments by a partition 31. A gas mixture of tetraethoxyorthosilicate (TEOS) and ozone is supplied from a gas inlet 15 to one of the compartments to process the substrates 4. Oxygen is supplied from a gas inlet 18 to the other compartment and is made into plasma 20 to plasma-process the substrates 4. Outlets 29 and 30 are provided on the sides of both compartments, respectively.
With this apparatus, however, the processing gases in both compartments enter mutually due to rotation of the holder 2 and a gap formed above the partition 31, and the processing gases chemically react not on the wafers but in the above space to produce products. The products formed in the space do not constitute material of the film formed on the wafers, but fall down onto the substrates 4 and become contaminant.